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  #1  
Old 06-14-2003, 10:10 PM
zander300e
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Question Conversion to R-134a

What, if any, parts need to be swapped out to convert a '91 300e from R-12 to R-134a??

Also, does anyone know if the original a/c compressor oil on the '91 is synthetic or petroleum based??

thanks!
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  #2  
Old 06-15-2003, 11:21 AM
LarryBible
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The oil in an R12 system such as yours is always Mineral oil.

The 124 MB is one of the very worst candidates for conversion to R134. Why are you wanting to convert? If you have a leak, it would be simpler and much less expensive to simply repair the leak, evacuate and recharge.

If you insist on converting, the entire system needs to be dismantled, the system thoroughly flushed to remove old oil, 134 compatible o-rings used with nylog sealant, the compressor removed, emptied and oil flushed with Ester oil, put in correct amount of ester oil, conversion fittings installed, new filter drier, evacuated and charged with 80% of the original volume with 134. If you want it to have a chance to cool well in stop and go traffic, you should also throw out the original serpentine condensor and replace with a parallel flow.

Some will tell you to get a conversion kit from Wal Mart. These are called Death Kits by many for good reason. Your a/c would last a short time should you take this approach.

R12 is coming down in price. Repair your leak, charge with R12 and you will be money ahead, as well as have an a/c that will actually keep you cool.

Good luck,
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  #3  
Old 06-15-2003, 11:40 AM
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< >>

Big improvement w/parallel..
A cheap trick for border-line condensors in hot climate is to jump the low fan dropping resistor... this gives you more air [high fan] in stop/go traffic.. not a big difference , but some ..
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  #4  
Old 06-16-2003, 08:24 AM
LarryBible
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There is another reason that these cars are poor candidates for 134 conversion. The oils used with 134, combined with the 134 are corrosive to copper materials. The original 124 evaporators are a combination of copper and aluminum. Given that this is in the flat rate manuals as a 15 1/2 hour job, I sure wouldn't want to do anything to accelerate the failure of this part.

Good luck,
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  #5  
Old 06-16-2003, 01:54 PM
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The A/C system in my 1990 300E stopped working a year ago. After a couple of estimates of $1,000-$2,000 for a "proper" repair, I decided that I would live without it for a while and eventually replace the car.

With nothing to lose, I installed a Walmart "Death Kit". I'm very happy with it and it is still cooling very well after 6 months of daily use.
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  #6  
Old 06-16-2003, 02:16 PM
LarryBible
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Dalton,

I am jealous of your good luck. For just a llittle more, you could've found your leak, repaired it, poured in a little Ester, evacuated and charged. That will up your chances of system life dramatically.

It's not too late, to recover, oil, evacuate and charge.

Have a great day,
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  #7  
Old 06-16-2003, 02:31 PM
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My A/C system was completely dry. All R12 and oils were gone(leaked out). I had the option of $1000(dealer) for R12 or $55(from a mechanic I know) for R134a. No one in my area sells R12. Now My ac is freezing cold with the R134a and I saved myself some $$$.
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  #8  
Old 06-16-2003, 02:44 PM
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Quote:
Originally posted by LarryBible
Dalton,

I am jealous of your good luck. For just a llittle more, you could've found your leak, repaired it, poured in a little Ester, evacuated and charged. That will up your chances of system life dramatically.

It's not too late, to recover, oil, evacuate and charge.

Have a great day,
This for me ??
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  #9  
Old 06-16-2003, 03:12 PM
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I would stick with R12. I had my system changed to R134 and I have never been happy. I hope to have it converted back this week. This is on my 89 300SEL. The A/C is ice cold going down the highway but in stop and go trafic you might as well be riding with the windows down. When I did my change over, I had the entire system replaced .
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  #10  
Old 06-16-2003, 05:08 PM
LarryBible
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Arthur,

I offer my apologies. I meant for that message to be 300EE320.

mike690003,

Even though the system was empty, if you charged it with a death kit it was not evacuated. Without evacuation there is a large amount of moisture that you are introducing the 134 into. This moisture combines with the refrigerant to make an acid that will eventually eat through your evaporator and other components from the inside out.

This is one of the biggest reasons that these are death kits.

Good luck,
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  #11  
Old 06-16-2003, 05:11 PM
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Here is my take on the subject (having converted four cars so far) I will use my W201 as a test case.

Larry is right, the R134 coolant/oil is not kind on the stock evaps, given that, it should be replaced for one of the updated units. The AC filter does need to be replaced as well. As for O Rings, the stock, MB updated rings work fine (although I bet they are designed for R134 retrofits) so pick up the new O Rings at the local MB dealer and replace them all.

The Wal Mart kits mentioned here are actually good kits, they include a pressure guage, pre-mixed coolant/oil and R134 adapter fittings. The R134 oil can co-exist with the R12 oil but a good rule of thumb is to drain as much of the R12 oil out as you can. The 80% fill ratio is accurate as R134 is a higher pressure coolant than R12.

On my W201, I replaced all the O rings, AC filter, AC filter sensor (was bad) evaporator (newer design) and new condenser. Replacing these components addressed the majority of the R12 oil left in the system. I filled my system to 80% capacity and added a can of Maxi-Cool, which as I understand it, is suppose to increase cooling of the R134.

I did this over two years ago and my system at full (with recirc on) blows right around 45-47 degrees and I have had no issues to date.

To sum this up, I was at my local MB dealer about a year ago and a gentleman came in for a R134 retro on a W124, the dealer charged him $1200 for this. I happened to be waiting right by a window into the shop, the W124 pulled into the stall where I was sitting. The MB tech evacuated the R12, drained the R12 oil from the compressor (or so it appeared) replaced the AC filter and replaced one AC line and some O rings (not sure how many) and then charged it up with R134, tested pressure and measured functional temp and he was done. Pretty interesting.
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  #12  
Old 06-20-2003, 03:52 AM
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i bought one of those walmart kits, but ended up
returning it since i cannot attach the connector with
the gauge to my low side. any tricks?
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  #13  
Old 06-20-2003, 04:20 AM
Benz300
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Gentlemen,
I had posted a similiar issue last week. I need to have my '87 260E a/c charged. And i do plan to stick with r12 since everyone i've had a quote from so far are asking around $1000 or so to do the conversion. No one wants to do it without converting since they all claim that R12 is no longer available. And the one person who does have it said he'll have to evacuate all of the old R12 and fill it back in which will cost me around $400. I live in NJ. and would like to know if anyone knows of a good mech/shop where I can get my A/C charged without spending $400 to $1000 and stick to the R12 type ?
thanks !
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  #14  
Old 06-20-2003, 10:46 AM
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Joel, the kits ususally come with R134a fittings that screw onto your old low/high side fittings. If you did not get these R134a fittings, you should be able to purchase them from the same place you picked up your R134a coolant. These fittings also come with a R134a conversion sticker which is suppose to be filled out and stuck right near the original R12 fill capacity sticker is
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  #15  
Old 06-20-2003, 11:58 AM
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2phast, thanks for the reply. my car was retrofitted
5 years ago and seems to be needing 134a refrigerant.
i just cannot push in the black plastic connector of
the gauge onto my fitting. i know i have to pull the
outer plastic until i got both ends connected.
i will re-purchase kit and re-try.

benz300, local shops here charge about $300 to
retrofit a/c, i paid $800 for my car since it incluced a re-built
compressor and new serpentine belt. shop around.
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